Crystallographic direction related spin current transmission in MgO(001)/Fe0.79Si0.21(001)/Pt(111) epitaxial bilayers

Spin-pumping and spin-orbit torque efficiencies in ferromagnetic/heavy metal bilayers, which usually consist of the polycrystalline grains, are related to the spin current transmission from ferromagnets to heavy metals and vice versa, respectively. In this work, epitaxial Fe0.79Si0.21(001)/Pt(111) films were fabricated to investigate the spin-pumping efficiency and spin-orbit torque efficiency by ferromagnetic resonance and harmonic Hall resistance measurement techniques, respectively. Ferromagnetic resonance results show that the incremental magnetic damping constants in epitaxial Fe0.79Si0.21(001)/Pt(111), compared with those of the epitaxial Fe0.79Si0.21(001)/AlOx reference sample, depend on whether the external magnetic field is applied along the in-plane easy or hard axes of Fe0.79Si0.21. The Pt thickness-dependent anisotropic damping constant was ascribed to the anisotropic spin current absorption in epitaxial Pt(111) layer. When electric currents were applied along the easy and hard axes of Fe0.79Si0.21 in epitaxial Fe0.79Si0.21(001)/Pt(111) bilayers, a large difference between spin-orbit torques generated from Pt(111) was observed by a harmonic Hall resistance measurement method. Both of the results suggest that spin current transmission efficiency is related to the anisotropic spin Hall effect of epitaxial Pt(111) layer due to the different spin-orbit interaction energies along the different crystallographic directions of Pt.

Automated summary

This study investigated the spin-pumping and spin-orbit torque efficiencies in ferromagnetic/heavy metal bilayers, revealing the influence of different crystallographic directions on the anisotropic spin current absorption and spin-orbit torques in epitaxial Pt(111) layer. The results from ferromagnetic resonance and harmonic Hall resistance measurement techniques provided insights into the spin current transmission efficiency and anisotropic spin Hall effect of the epitaxial Pt(111) layer.